1. Field of the Invention
The present invention relates to an ionization method and apparatus using electrospray, and to an analyzing method and apparatus.
2. Description of the Related Art
A typical method of imaging mass spectrometry for dealing with biological samples and industrial products and the like is mass spectrometry using matrix-assisted laser desorption ionization (MALDI). With this method, a pretreatment, namely the preparation of a MALDI sample, is required.
The molecular analysis of live single cells has been gaining momentum in recent years, and nano-electrospray (ESI) mass spectrometry has been proposed as an effective analytical method for this purpose.
See Mizuno, Tsuyama, Harada and Masujima “Live single-cell video-mass spectrometry for cellular and subcellular molecular detection and cell classification”, J. Mass Spectrom. 2008; 43: 1692-1700.
According to this method, a cell of interest or cellular solution thereof is drawn into the end of a glass ESI tip (a capillary), the end having an opening diameter (inner diameter) on the micron order, an ionization solvent (for example, acetonitrile containing 0.5% formic acid for the positive-ion mode, or 0.5% ammonia water for the negative-ion mode) is applied to the interior of the ESI tip to achieve dilution by 106 times or more, then the diluted cellular sample is ionized by electrospray and the result introduced to an analyzing apparatus. With this method, the solvent also undergoes mass spectrometry as a matter of course, and an ion signal ascribable to molecules resulting from the solvent shows up in the mass spectrometry spectra.